NuGet upgrade issue

Solution 1:

1. Close all visual studio 2010 instances.
2. Open visual studio again as administrator
3. Go to "Tools" > "Extension Manager"
4. Uninstall NuGet
5. Install NuGet again.

if you are not able to uninstall it go to:

C:\Program Files (x86)\Microsoft Visual Studio 10.0\Common7\IDE\Extensions\Microsoft Corporation\NuGet Package Manager

and remove this folder. deleting this is at your own risk!

Solution 2:

This is documented on our Known Issues page: http://docs.nuget.org/docs/reference/known-issues

There's two reasons why you might run into this issue. You've installed an unsigned or wrongly signed version of NuGet. For example, if you grab a build off of our continuous integration server (http://ci.nuget.org/) or if you installed one of our previous CodePlex releases.

There's another issue affecting some users of Windows XP or Windows 2003 where it appears the certificate authority on the machines are incorrectly reporting the certificate as not valid. We're still investigating this issue.

Solution 3:

From NuGet page on VS Gallery website:

"Review current release notes/known issues on the NuGet Docs site, including details and solution for about a common upgrade failure (Visual Studio 2010 SP1 Hotfix available)"